Investigate by means of risk factor analysis whether minimal breast cancer in initially asymptomatic women is essentially different from clinical breast cancer whether it is an early manifestation of the same disease and to compare prevalent to incident breast cancer cases in order to identify risk factors associated with tumor aggressiveness. To accomplish these, we will analyze data collected by the Guttman Breast Diagnostic Institute which since 1968 has been offering free breast examinations to women living in New York City. Cases will be compared according to three tumor criteria: level of invasiveness, level of aggressiveness, and histological type. If risk factors related to higher malignancy (invasiveness) and rapid growth (aggressiveness) are identified, then future screening efforts can be redirected towards detecting these biologically important breast cancers.